The current epidemic rate of childhood obesity is a leading health concern as overweight/obese youth may suffer from comorbid conditions, once considered exclusive to adults. It has been suggested that physical inactivity is a major determinant of obesity and obesity-related health risk in children and adolescents. Recent studies in adults report that the combination of aerobic and resistance exercise is a better strategy than aerobic or resistance exercise alone for reducing risk factors for type 2 diabetes. Currently, the most effective exercise modality for concurrent reductions of adiposity, in particular abdominal fat, and risk factors for type 2 diabetes and cardiovascular disease (CVD) is unknown in adolescents. Therefore, we will employ a randomized trial to examine the effects of a long-term aerobic exercise, resistance exercise, and a combination of both exercise regimens on: 1) in vivo insulin sensitivity, glucose tolerance and risk for type 2 diabetes, 2) total adiposity, skeletal muscle mass, visceral adiposity and ectopic fat in the liver and skeletal muscle, and 3) traditional and non-traditional risk factors/markers for CVD in overweight boys and girls. We will recruit 168 sedentary overweight (BMI >85th percentile) adolescent boys and girls aged 12-17 years old and randomly assign them to one of three 6-month intervention groups (n = 56 each group): 1) aerobic exercise (180 min/week), 2) resistance exercise (180 min/week), or 3) aerobic and resistance exercise (180 min/week) group. A weight maintenance diet (55-60% carbohydrate, 15-20% protein, and 25-30% fat) will be prescribed and monitored for all groups, so that any changes in energy balance will be induced by exercise intervention alone (e.g., no calorie restriction). We believe that this proposed application will have a significant implication that is directly relevant for one in three American adolescents who are at increased risk of developing obesity-related co-morbidities.